Positive displacement piston pumps are well known in the art. Typically, piston pumps are comprised of a plurality of cylinders containing pistons that travel in and out of the cylinder bores. The cylinders are in fluid communication with the pump's intake or suction port as well as the pump's output or pressure port. The cylinders have mechanical valving to enable or disable the flow from either the pump's suction or pressure ports. Two types of mechanical valving are well known in positive displacement piston pumps. An example of the first type of mechanical valving is a valve plate which will enable the required timing of fluid communication as a cylinder block rotates. The second type of mechanical valving comprises check valves. In a positive displacement piston pump utilizing check valves, the check valves alternately open and close to allow fluid into and out of the piston bores, as the pistons reciprocate into and out of the cylinder bores, thus performing the pumping function.
One disadvantage of the mechanical valves used to control the flow of transmission fluid through cylinders of conventional piston pumps is that they comprise many moving parts. Typical check valves include moving poppets and springs, all of which add to the cost of the piston pump. Further, these components can degrade over time, causing inefficient pump performance or failure. As such, there is a need in the art for a positive displacement piston unit that does not rely on conventional mechanical valving, thereby minimizing cost, improving reliability, and for other useful purposes.
Magnetorheological (MR) and electrorheological (ER) fluids have often been used in various pumping capacities, as disclosed in U.S. Pat. No. 2,651,258 to Pierce. MR fluids are those that change viscosity or even substantially solidify in the presence of a magnetic field. ER fluids behave similarly in the presence of an electric field. Because of their characteristics, MR and ER fluids have been used as transmission fluids as in Pierce, without the need for mechanical valves to control their flow. These fluids have commonly been used in brake systems as well as the active fluid in shock absorbers. To a much more limited extent, these fluids also have been used with piston pumps, as disclosed in U.S. Pat. No. 5,409,354 to Stangroom. Stangroom teaches the use of ER fluids in a mechanism triggering the opening and closing of a check valve. Stangroom does not, however, teach the use of MR and ER fluids as transmission fluids.
It is therefore a principle object of this invention is to provide cylinder valves that utilize a minimum number of moving parts and resist wear over the life of a positive displacement piston unit.
A further object of this invention is to provide a positive displacement piston unit that employs magnetorheological or electrorheological fluids to control the operation of the cylinder pistons and the hydraulic power transmission of the piston unit.
These and other objects will be apparent to those skilled in the art.